Purging Vim undodir

31 July 2012

In two weeks, it would be the second anniversary of vim 7.3 release. Among other things, that release brought a nice feature of persistent undo. Here’s a short excerpt from :help persistent-undo for those who didn’t hear of it before:

When unloading a buffer Vim normally destroys the tree of undos created for that buffer. By setting the ‘undofile’ option, Vim will automatically save your undo history when you write a file and restore undo history when you edit the file again.

Undo files are normally saved in the same directory as the file. This can be changed with the ‘undodir’ option.

NOTE: undo files are never deleted by Vim. You need to delete them yourself.

The last note is the reason I wrote this post. Using vim as my $EDITOR of choice, I tend to pollute undodir a lot: Git commits, experiments in /tmp and /var/tmp, refactoring of code bases — all that generates a lot of undofiles that I would never use again, simply because I deleted the original files.

I googled for existing solutions and it seems that people just run something like rm -rf ~/.vim/undofiles/ once in a while, but that’s not the best solution ever: losing history that I may need later makes me a little nervous.

Some other people use quite more wise yet bad solution: they run find ~/.vim/undofiles -mtime +7 -delete, deleting everything that is more than seven days old. While effective against undofiles associated with temporary files, it’s still a risk: there’s scripts that I rarely edit, still I want to preserve all the history, just in case I need it.

So I present you yet another solution: shell script that removes only those undofiles that are no longer needed, i.e. does not have associated files in the filesystem anymore. It is intended to be run as a cron job. Without further ado, here’s the code:

Just copy the code to a file named purge_vim_undodir, put it somewhere and set executable flag (using chmod +x purge_vim_undodir). Then edit your crontab using crontab -e. You can come up with your own timing, or just use the one I propose in comments to the script. That’s it — from now on, your undodir would be cleared automatically, only containing files that it is worth storing.

Hope you’ll find that useful.

Update (27.08.2012): add a comment about the newline at the end of crontab file.